need some advise on new installation/upgrade

I have Plesk (7.1.5) running on FreeBSD 4.9. I want to upgrade to the latest Plesk, v. 7.5.2 on a new server.

Do you have some advice howto accomplish this? I mean is it wise to use install FreeBSD 5.3 and Pleask 7.5.2 on the new server, backup 7.1.5 (via psadump or something) and import it on the new server? OR install FreeBSD 4.9 and plesk 7.1.5 -> put the backup back, and upgrade to freeBSD 5.3 and 7.5.2. (I know upgradeing from bsd 4.9 to 5.3 isnt very good to do, because these are 2 'different' OS's)